The present invention relates to an EVA (ethylene vinyl acetate copolymer resin) insole manufacturing processes, and more particularly to an EVA insole manufacturing process where an EVA resin is mixed with a foaming agent for making a molding by an injection molding machine, and the thus obtained molding is foamed in a mold, so as to obtain an insole immediately after form setting without any further cutting, trimming or grinding procedure.
In a conventional EVA insole manufacturing process, an EVA resin is mixed with a foaming agent, and the mixture is then squeezed into strips. The EVA material strips are then placed in a hot press and subjected to a foaming process. After foaming, the foamed EVA strips are placed in a water cooling trough for cooling. After cooling, the foamed EVA strips are cut and trimmed, or sometimes, some pieces of trimmed EVA pieces are adhered together. After passing through a grinding process, the EVA strips thus obtained are placed in a hydraulic machine for form setting. Thus, a whole EVA insole manufacturing process is completed. This EVA insole manufacturing process is not satisfactory, because of the following disadvantages:
1. It requires much human power. In a complete production line, there are generally more than 30 experienced workers required.
2. Much waste material is produced. Because EVA strips are cut and sheared after the foaming process, approximately 40% or more of the foamed EVA strips are cut off and become useless. Disposal of the waste material is still a problem to settle, and it may cause environmental pollution.
3. It consumes much time (about 3 or more days) to produce a specific style of an EVA insole. Therefore, it is not suitable for producing various styles or designs of EVA insoles at a time.
4. If an insole is comprised of several EVA strips of different hardness bound together, an insole may tear easily due to weak structural strength.